1. Field of the Invention
The present invention relates to a method for dry etching a multilayered film, and more specifically, relates to a dry etching method for processing an alumina (Al2O3) film having a thickness of 200 nm to 1000 nm arranged on a nickel chrome (NiCr) alloy film, in which a ruthenium (Ru) film is used as mask to process the Al2O3 film with high selectivity to obtain a perpendicular process shape.
2. Description of the Related Art
When processing Al2O3 films having a thickness of 200 nm to 1000 nm used for forming magnetic heads in a dry etching apparatus, a nonvolatile material such as NiCr alloy film or the like is used as the mask material to achieve the required selectivity. This NiCr alloy film is nonvolatile, and is difficult to process via dry etching, so it is conventionally processed via milling. However, along with the miniaturization of the processing object, milling processes have become more and more difficult due to drawbacks of accuracy and processing rate. Therefore, studies are now being performed to process the mask material and the Al2O3 film via dry etching.
In other words, it is necessary to find a mask material that enables the mask and the Al2O3 film to be dry-etched and has high selectivity with respect to the Al2O3 film.
FIG. 5 is referred to in describing a processing method using an NiCr alloy film as mask material.
FIG. 5(a) is a cross-sectional view of a wafer prior to the etching process. The wafer includes, from the upper layer in the named order, a patterned resist mask 11, an upper layer NiCr alloy film 15, an Al2O3 film 14 and a lower layer NiCr alloy film 15. At first, the milling process of the upper layer NiCr alloy film 15 performed under conditions using a fluorine-based gas causes the surface layer portion of the Al2O3 film 14 to be etched for approximately 80 nm in a tapered shape, and thus, it becomes difficult to fine-process the NiCr alloy film (FIG. 5(b)). Next, when the Al2O3 film 14 is dry-etched in a low pressure range using a gas mixture containing boron trichloride (BCl3), chlorine (Cl2) and argon (Ar), the etching proceeds with the surface layer portion of the Al2O3 film 14 still tapered by the milling process, so the processing shape of the Al2O3 film will be tapered and could not be etched perpendicularly (FIG. 5(c)).